There is known of an EGR device that allows for preventing knocking and improving fuel economy performance by recirculating a portion of exhaust air onto an intake side thereof as EGR gas. The EGR device is generally configured including: an EGR passage branching out from an exhaust passage and joining to an intake passage; and an EGR valve disposed in the EGR passage adapted to open and close to control an EGR gas amount. When performing EGR control in which the EGR gas is introduced, a controller of the internal combustion engine opens the EGR valve to achieve a target EGR ratio set in accordance with an engine operating state. However, a delay occurs from when the EGR valve is opened to until the actual EGR ratio reaches the target EGR ratio; hence, if an ignition timing is switched to one according to the target EGR ratio simultaneously to the opening of the EGR valve, knocking will occur. Accordingly, the controller calculates an estimate EGR ratio on the basis of for example a position of the EGR valve and engine rotation speed, and controls the ignition timing in response to the estimate EGR ratio, to prevent the knocking.
When an EGR control non-performed state continues, a part of the EGR passage from a joining portion with the intake passage to the EGR valve is filled with fresh air. When the EGR control is started at this state, only the fresh air will be pushed outside to the intake passage for the first while, even if the EGR valve is opened, and the EGR gas will not be introduced into the intake passage. Therefore, until a pipe from the EGR valve to the joining portion is filled with EGR gas, a divergence will generate between the actual EGR ratio (true EGR ratio) and the estimate EGR ratio; at an ignition timing set on the presumption of having a higher estimate EGR ratio than the true EGR ratio, the knocking would occur.
In JP2007-278116A, in order to prevent the above divergence between the true EGR ratio and estimate EGR ratio, a valve is further provided at the joining portion of the EGR passage and the intake passage, to fill the pipe between that valve and the EGR valve with EGR gas. This introduces the EGR gas into the intake passage immediately after the start of the EGR control, and thus allows for preventing the divergence between the estimate EGR ratio and the actual EGR ratio.